Question

What is the sum of the arithmetic sequence 152, 138, 124, …, if there are 24 terms?

Answer 1

(24/2){2(152) + (24-1)(-14)} = -216. -216 is the sum of the sequence.

Answer 2

hello :
124-138=138-152 = -14 (common diference)
the sum of 24 terms is : S = n/2( U1 +U 24 )
n= 24 U1 = 152
Un = U1+(n-1)d ..... d = -14
n=24 : U24 = 152+(24-1)(-14) =152-322 = -170
S= 24/2(152-170) = 12(-18) = - 216